docs: def get_site_amplification(self, C, sites):
          """
          Returns the linear site amplification term depending on whether the
          Vs30 is observed of inferred
          """
          ampl = np.zeros(sites.vs30.shape)
          # For observed vs30 sites
          ampl[sites.vs30measured] = (C["d0_obs"] + C["d1_obs"] *
                                      np.log(sites.vs30[sites.vs30measured]))
          # For inferred Vs30 sites
          idx = np.logical_not(sites.vs30measured)
          ampl[idx] = (C["d0_inf"] + C["d1_inf"] * np.log(sites.vs30[idx]))
          return ampl